Radio contribution to the NOEMA continuum emission around W3 C. Left: VLA 22.5 GHz radio continuum observations from Tieftrunk et al. (1997) rescaled to 220 GHz (see text for details). W3 C is in the centre, with weak emission from W3 IRS4, highlighted with a white dashed circle, to the NE and W3 D further away to the NW. Middle: NOEMA 220 GHz continuum emission. Right: NOEMA continuum map after the free–free contribution has been estimated from the VLA observations and removed (see text for details). All data were convolved to the same 0.8 × 0.8′′ beam. The black contours indicate intensity iso-contours at 5−30σ (σ = 0.4, 0.8 and 1.4 mJy beam⁻¹ from left to right), increasing in 5σ increments, with the addition of a lower contour at 3σ for the VLA observations to show that the weak emission at the location of W3 IRS4 is significant. The white-dashed contours indicate −5σ_rms.